Vehicles may be fitted with emission control systems wherein vaporized hydrocarbons (HCs) released from a fuel tank (for example, during refueling) are captured and stored in a fuel vapor canister packed with an adsorbent. At a later time, when the engine is in operation, the evaporative emission control system may use a vacuum (or pressure) to purge the vapors into the engine intake manifold for use as fuel. The purge flow vacuum (or pressure) may be generated by one or more pumps and/or ejectors.
One example approach for providing sufficient vacuum for a fuel purge flow is illustrated by Kakimoto et al. in US 2006/0196482 A1. Herein, blow-by gas and purge gas are delivered to the engine intake together. Specifically, blow-by gas is pumped to the engine intake through an ejector in such a manner that a fuel vapor purge flow is also sucked into the intake by using a negative pressure (that is, vacuum) generated by the high-speed flow of the blow-by gas through the ejector.
However, the inventors herein have recognized potential issues with such an approach. In one example, pump operation is necessitated for generating a vacuum at the ejector and for drawing a purge flow, irrespective of whether the engine is boosted or not. Thus, due to dependence on pump operation for purging, during conditions where pump operation is limited or restricted, a purge flow may not be possible. Additionally, the need for constant pump operation during purging may add to fuel costs while decreasing pump life. In another example, a flow of blow-by gases is necessitated for generating the vacuum at the ejector and for drawing the purge flow. Thus, during purging conditions when a flow of blow-by gases to the intake is not desired, or not available, a purging operation may not be performed. In still another example, the vacuum generated at the ejector may only be used for drawing a purge flow. Thus, an alternate vacuum actuator, such as a power brake, may not be operated using the ejector vacuum during a purging operation. Thus, an additional pump and/or ejector may be required to generate the vacuum required for the power brake. As such, this may increase component cost.
Thus, in one example, some of the above issues may be addressed by a method of operating a boosted engine system including a fuel vapor canister, a purge pump, and an ejector. In one embodiment, the method may comprise pumping a purge flow through the fuel vapor canister, then through the ejector, and then to an engine intake, and applying vacuum from the ejector to a vacuum actuator.
For example, a purge pump and at least one ejector may be configured in series and may be coupled between an engine intake manifold and a fuel vapor recovery system such that, during a boosted engine operation, a flow of air and/or fuel vapors may be pumped to the engine intake through the ejector, thereby creating a vacuum at the ejector. In one example, during purging conditions, a canister vent valve may be opened and the purge pump may be operated to pump a fuel vapor purge flow through the fuel vapor canister, then through the ejector, and then to the engine intake. By pumping a purge flow through the ejector before delivery of the purge flow to the engine intake, a vacuum may be advantageously generated at the ejector during boosted engine operation. This vacuum may be applied from the ejector to a vacuum actuator, such as a power brake and/or a wastegate actuator. As such, additional secondary ejectors may be coupled to the primary ejector to further deepen the generated vacuum. In this way, during purging conditions, a purge pump may be operated to provide a vacuum for drawing fuel vapors and also for actuating a vacuum actuator.
In another example, during a non-purging condition, the canister vent valve may be closed, a vapor bypass valve may be opened, and the purge pump may be operated to bypass the fuel vapor canister and pump air (e.g., fresh air not mixed with fuel vapors) through the ejector to the engine intake. The vacuum generated by the pumping of air through the ejector, may be applied from the ejector to the vacuum actuator. In this way, during non-purging conditions, the purge pump may be operated to provide a vacuum for various vacuum actuators. In comparison, when the engine is not boosted, the intake manifold vacuum may be applied to draw a purge flow from the fuel vapor recovery system during purging conditions, without operating the purge pump. Similarly, during purging and non-purging conditions, intake manifold vacuum may be applied for vacuum actuator actuation.
In alternate examples, the pump may be located upstream or downstream of the fuel vapor storage canister. In either pump configuration, the ejector may be located with its exit flowing towards a low pressure.
In this way, a purge flow may be drawn to an engine intake, in the presence or absence of engine boost, without requiring constant purge pump operation. Further, the purging operation may be performed independent of a blow-by gas flow. Specifically, in the absence of boost, an engine intake manifold negative pressure may be used to draw a purge flow, while a purge pump may be used to draw a purge flow in the presence of boost. Additionally, a vacuum may be drawn at the ejector coupled downstream of the pump during every purging operation. Specifically, by pumping the purge flow through an ejector before delivering purged fuel vapors to the engine intake, a vacuum may be generated at the ejector during boosted conditions, which may be advantageously used for actuating additional vacuum actuators. Consequently, the need for dedicated vacuum pumps for the vacuum actuators may be reduced. Alternatively, the purge flow driven vacuum may be used in addition to a dedicated vacuum pump, enabling the use of a smaller vacuum pump for the vacuum actuator and/or a shorter duration of vacuum pump operation. By enabling purging and vacuum actuation under most engine operating conditions, vehicle fuel economy and emissions may be improved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.